Abstract :
After a brief historical introduction this article will present a summary of experimental work
carried through at Penn State to explore the flexoelectric coefficients μijkl in ferroelectric,
incipient ferroelectric and relaxor ferroelectric perovskites. The initial objective was to
understand the magnitude of flexoelectricity in these systems to see whether it would be
possible to develop a piezoelectric composite containing no piezoelectric element, which
nonetheless could have practically useful properties. Recent discussions of the thermodynamic
converse effect, ie. the generation of elastic strain by an electric field gradient, now suggest that
such composites might be designed to have unique properties such as a direct but no converse
effect, or vice-versa, and materials with this character could have important practical
application. Present data already suggest that the direct effect may make an important
contribution to the properties of epitaxial thin films where mismatch can give rise to very steep
elastic strain gradients. Clearly, more work is needed to fully quantify the flexoelectric behavior.
It will be important to measure single crystals in the ceramic systems which have been studied
and to characterize the converse effect as a check of the measured values.
C 2006 Springer Science + Business Media, Inc.
